(1) Field of the Invention
This invention relates to a photographic apparatus such as a video camera, and a photographic method using this apparatus. More particularly, the invention relates to a photographic technique for use in scientific measurement concerning fast moving bodies such as rockets, explosion, turbulence, electric discharge, movement of microbes under a microscope, and signal transfer of the brain and nervous system.
(2) Description of the Related Art
A conventional high-speed photographic apparatus (high-speed video camera) has fixed photographing intervals, i.e. a fixed photographing speed, when performing a series of photographic operations. At a moment a phenomenon occurs with a photographic subject, the occurrence varies rapidly. It is therefore desirable to photograph the photographic subject at short intervals, i.e. at high speed, in order to secure detailed results. On the other hand, before or after the occurrence of a phenomenon, variations are slow. It is desirable to photograph the photographic subject at relatively long intervals, i.e. at low speed. The term “photographing interval” used in this specification represents time per unit frame (the unit being seconds per frame). The “photographing speed” represents the number of frames per unit time (the unit being frames per second). That is, the photographing speed is the inverse of the photographing interval.
(I) However, with a high-speed camera having a fixed photographing speed, short photographing intervals resulting in an increased amount of photographic data, or a limited memory capacity, makes a whole series of photographic operations impossible. Conversely, long photographing intervals will result in a failure to photograph rapid variations.
(II) When obtaining image information for checking variations occurring with a photographic subject in greater details, that is when obtaining image information for a plurality of frames in a unit photographing time, as shown in the timing chart of FIG. 1, a light source is driven a plurality of times (three times in FIG. 1) to illuminate the photographic subject within one exposure time t1. In this case, it is necessary to use a special laser light as the light source in order to illuminate the subject at minute intervals with high accuracy.
Since the unit photographing time and exposure time are fixed for a series of photographic operations, that is since one exposure is carried out within the exposure time, image information cannot be obtained to reflect variations occurring with the photographic subject with high accuracy. When photographing an explosion accompanied by self-flashing, for example, rapid variations accompanied by flashing take place at a moment of occurrence of the phenomenon. Therefore, an exposure time for avoiding halation due to an excessive quantity of light entering the device is taken into account, and a short unit exposure time is set. However, after the occurrence of the phenomenon, photography is continued with the same conditions despite a reduction in the quantity of light by flashing and a slackening in the variations of the phenomenon. Consequently, dynamic images all clear from beginning to end cannot be obtained based on a series of image information obtained.
When obtaining image information for a plurality of frames in a unit photographing time, a multiple exposure is carried out by driving the light source a plurality of times during one exposure within the unit photographing time. Thus, all the image information obtained from one exposure is displayed in superimposition on one image. As a result, it is difficult to distinguish and check image information on the dynamic image.
Since the conventional apparatus has the unit photographing time and exposure time remaining fixed for a series of photographic operations, it is a complicated operation to set optimal conditions for photographing a photographic subject, with an additional drawback of increased cost. That is, in order to obtain clear image information, duplication experiment must be carried out by varying the exposure time a plurality of times before production photography.